JPH0125144B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a method for manufacturing a magnetic recording medium with a high S/N ratio and suitable for high-density magnetic recording.

In recent years, with the aim of increasing the density of magnetic recording, research has been conducted on thin metal film magnetic recording media in which cobalt-based alloys are formed on substrates using methods such as plating, sputtering, ion plating, and vacuum evaporation. N
Regarding the characteristics, only the effects of surface properties have been studied, and no analysis of noise related to magnetic materials has been conducted, so it has only been confirmed that the output is improved compared to conventional coated media. figure,
Currently, the S/N ratio, which determines practical performance, has not improved very much.

In the case of coated magnetic recording media, the guidelines for improving the S/N are almost clear: increasing the strength of coercive force and magnetization, improving surface properties, reducing the size of magnetic powder, and improving the acicular ratio. Efforts are being made to improve the S/N ratio by increasing the ratio, improving dispersibility, and improving orientation.

On the other hand, in the case of metal thin film media, the only ways to improve output are to reduce the surface roughness, to increase the strength of coercive force and magnetization, and to reduce noise, the only methods known are to improve the surface properties. It is just an analogy from the type medium.

As a result of many experiments, the inventor of the present invention discovered that the size of the demagnetized magnetic domain of a metal thin film magnetic recording medium whose main components are cobalt and oxygen is essentially related to the S/N. In other words, if a magnetic layer is used in which the size of the demagnetized domain is 0.3μ or less when measured perpendicular to the direction of magnetic recording, the noise will be significantly reduced, and if it is 0.03μ or less, the output will decrease. It is based on

Although it cannot be said that the above reason has been fully elucidated academically yet, the present inventor estimates as follows.

In other words, in the case of metal thin film media, magnetic recording and reproduction is performed by transforming random demagnetized magnetic domains into highly periodic recorded magnetic domains during recording, but there is a correlation that the larger the demagnetized magnetic domains, the rougher the recorded magnetic domains. , it is thought that the random leakage magnetic field from the domain wall becomes larger and the noise increases. Conversely, regarding output, it is known that the larger the demagnetized magnetic domain, the stronger the ferromagnetic interaction inside the magnetic layer, but this increases the mobility of the domain wall, and the same coercive force and magnetization strength (in a DC magnetic field) It is estimated that the larger the demagnetized magnetic domain, the higher the recording efficiency (measured value).

In view of the above, the present invention aims to obtain a medium with dramatically improved S/N ratio as a result of analyzing the noise related to the magnetic material generated from the magnetic layer in the production of cobalt-based media by vacuum evaporation method. This was successfully achieved, and a detailed explanation will be given below using the drawings.

FIG. 1 is a schematic diagram of magnetic domains observed by the Lorentz method or Bitter method after bulk erasing a medium in which a thin film containing cobalt and oxygen as main components was formed on a substrate by vacuum evaporation. It is formed by oblique deposition so that it has magnetic anisotropy so that the direction of easy magnetization is approximately in the x direction in the figure, and magnetic recording is performed in the x direction. The direction perpendicular to the x direction is the y direction,
FIG. 2 shows measured data on the relationship between the width of the magnetic domain measured in the y direction, the relative output, and the relative noise level. The recording wavelength at this time was 2μ. As the magnetic domain width increases, the output increases and almost saturates at about 0.03μ or more. At this time, the noise level also increases gradually, but it increases sharply when the magnetic domain width is 0.3μ or more, and thereafter, when the magnetic domain width is doubled, the noise tends to increase at a rate of about 4 decibels. The sample used had a coercive force of 800 Oersteds and a film thickness of approximately 1000 Å, but the inventors have determined that the coercive force is between 400 Oersteds and 2000 Oersteds.
We confirmed that the film thickness ranged from 200 Å to 4000 Å, but the trends were exactly the same and there was no specificity, confirming that the limiting requirement for the medium is the width of the magnetic domain.

In the medium according to the present invention, magnetic recording and reproduction are performed by transforming random bulk erase magnetic domains M as shown in FIG. 1 into highly periodic recording magnetic domains during recording. The interaction is strong, so the mobility of the domain wall is large, and even with the same coercive force (measured in a DC magnetic field), the recording efficiency is high, and the output is high when the coercive force is 0.03μ or more.
Furthermore, the larger the magnetic domain, the larger the random leakage magnetic field from the domain wall, so it is thought that noise increases rapidly with a domain width of 0.3μ or more. For this reason, when using a magnetic layer made by vacuum evaporation method etc. whose main components are cobalt and oxygen, the size of the bulk erased magnetic domain is in the range of 0.03μ to 0.3μ when measured perpendicular to the direction of magnetic recording, the S/N ratio is It has now become possible to obtain a magnetic recording medium for high-density recording that has been dramatically improved.

Here, the conventional method and the method of manufacturing a magnetic recording medium according to the present invention will be explained based on specific experimental examples.

Experimental example 1 Deposition rate 1 to 1000 on a 20 μm thick polyester film at an incident angle of 0°, vacuum level of 1 × 10 ^-5 Torr
Cobalt was deposited at a substrate temperature of 10°C to 60°C. Since the coercive force is small at 50 to 100 oersteds, the output is also small at -20 to -25 dB on the scale shown in Figure 2, but the noise level is extremely high at +20 to +30 dB. Under this condition, the magnetic domain width was 200 μm to 500 μm.

Experimental example 2 On a polyester film with a thickness of 20 μm, the incident angle is 60° to 80°, the degree of vacuum is 1 × 10 ^-5 Torr, and the substrate temperature is 10°C.
Cobalt was deposited at ~60°C and a deposition rate of 1-1000 Å/sec. The coercive force was 100 to 1000 oersted, and the domain width was 2 μm to 30 μm. For those with a coercive force of 500 oersted or more, the output was close to 0 dB, but
Noise was high at +10 to +15dB.

Experimental example 3 An incident angle of 0° on a 30 μm thick polyimide film.
Argon partial pressure 1×10 ^-4 to 5×10 ^-2 Torr, speed 1
Cobalt was ion plated with DC and radio frequency at ~200 Å/sec. Although the coercive force was 500 to 1000 oersted, no magnetic domains were formed or the width of the magnetic domains was 0.03 μm or less. The noise is -
It was about 7dB, but the output was -5 to -6dB,
Bad S/N.

The above are the experimental results using conventional manufacturing methods, but these methods could not obtain the magnetic domain width according to the present invention. Next, the manufacturing conditions established by the present inventor will be explained.

Experimental Example 4 FIG. 3 is a schematic diagram of a vapor deposition apparatus used in the method of manufacturing a magnetic recording medium according to the present invention, in which 1 is a vacuum vessel;
2 is a cooling can, 3 is a base film unwinding machine, 4
5 is a winder, 5 is a base film such as a polyester film, 6 is a mask, 7 is a vapor deposition material, and 8 is a crucible. The vapor deposition material 7 is heated and evaporated by an electron beam or the like, and as the base film 5 travels along the circumferential surface of the cooling can 2 in the direction of the arrow, the incident angle decreases continuously from 90° until it reaches the minimum incident angle θ. It is deposited in the range of . At this time, oxygen gas or the like is introduced from the gas introduction nozzle 9 to control various characteristics of the deposited film. Next, FIG. 4 shows data obtained by analyzing the conditions for manufacturing a ferromagnetic thin film having a desired magnetic domain width using the apparatus shown in FIG. The horizontal axis shows the oxygen concentration in the deposited film, the minimum incident angle θ, the substrate temperature, and the nickel concentration when nickel is added to cobalt as the vapor deposition material, and the vertical axis plots the manufacturing factors that relate these conditions to the magnetic domain width. are doing. The domain width is approximately equal to the product of these five manufacturing factors expressed in microns. For example, when the oxygen concentration is 20%, the minimum incident angle is 40°, the substrate temperature is 60°C, the deposition rate is 1000 Å/sec, and the nickel concentration is 20%, the product of manufacturing factors is 0.37 x 1.01 x 1.05 x 0.6 x 0.42 =
0.1μ, and a magnetic recording medium with a high S/N ratio can be obtained.

As described above, due to the short history of metal thin film media, clear guidelines for improving S/N have not been obtained, but with the present invention, a phenomenon unique to metal thin film media has been discovered. It has become possible to obtain a medium with an unprecedented high S/N.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a bulk erase magnetic domain of a magnetic recording medium according to the present invention, where x is the magnetic recording direction,
y indicates the direction perpendicular thereto, and FIG. 2 is a diagram showing the relationship between the width of the bulk erase magnetic domain measured perpendicular to the magnetic recording direction and the output and noise characteristics of the medium.
FIG. 3 is a schematic diagram of a vapor deposition apparatus used to manufacture a magnetic recording medium according to the present invention, and FIG. 4 is an analysis of manufacturing condition factors for obtaining the magnetic domain width according to the present invention in the apparatus shown in FIG. FIG.

Claims (1)

[Claims] 1. A method for manufacturing a magnetic recording medium in which a thin metal magnetic layer containing cobalt and oxygen as main components is formed on a substrate, and the size of the demagnetized magnetic domain of the magnetic layer is measured perpendicular to the direction of magnetic recording. A method for manufacturing a magnetic recording medium, characterized in that the magnetic recording medium has a thickness in the range of 0.03μ to 0.3μ.